The present invention relates to hydraulic swaging devices for radially expanding tubular structures, and, more particularly, to a high-pressure swaging device wherein an adaptor is connected to a hydraulic pressure source through a lengthwise-flexible metallic conduit.
There are a variety of situations in which it is desired to expand a metal tube radially to form a tight, leak-free joint with a surrounding structure. For example, large heat exchangers, particularly of the type used as steam generators in power plants, often employ a tube sheet, which is a steel plate up to several feet thick, through which hundreds of stainless steel or carbon steel tubes must pass. The tube sheet is initially fabricated with bores of a suitable diameter into which the tubes are inserted. The tubes are then expanded against the sides of the bores by internally pressurizing the tubes to a sufficiently high pressure that they are plastically expanded into sealing contact with the bores.
A preferred approach for accomplishing the expansion of the tubes is insertion of a mandrel into the tube, the mandrel being sufficiently long that it spans the entire thickness of the tube sheet. The mandrel is provided with seals at either end to confine fluid pressure within the space between the mandrel and the inside wall of the tube, and is further provided with an external fluid connection. A source of high hydraulic pressure, at least about 30,000 psi and typically about 60,000 psi, is attached to the external fluid connection, and the space between the mandrel wall and the inside of the tube is pressurized. This high pressure plastically deforms the wall of the tube outwardly into sealing contact with the bore of the tube sheet, thereby sealing the tube into place. The hydraulic pressure is then released, the mandrel is withdrawn, and the process is repeated with the next tube.
In a typical power plant heat exchanger, there may be one thousand or more tubes in each heat exchanger, and each tube must be sealed into a tube sheet at each of its ends. Thus, it is necessary to repeat the expansion process many times, and it is highly desirable that such expansion process be rapidly and conveniently performed. Moreover, in some instances the tubes and tube sheets are located inside other structure and are relatively inaccessible.
Experience has shown that conducting the necessarily high pressure to each of a series of tubes is one of the most difficult aspects of the expansion process. In one approach, the hydraulic pressure source is itself moved from tube to tube. This approach is generally unsatisfactory, since the hydraulic pressure source is large and clumsy, and may be quite heavy.
In another approach, described in U.S. Pat. No. 4,362,324, the hydraulic pressure source is stationary, and pressure is conducted to the mandrel by a jointed high pressure conduit wherein a series of rigid sections are connected together with a plurality of movable joints. Such a conduit generally performs satisfactorily, but has several drawbacks. A large number of joints are required, requiring the use of many machined pieces and many seals. This conduit is therefore relatively expensive to manufacure, and may be subject to leakage at any of the seals. The conduit also may not be usable when the tubes and tube sheets are located within a tightly constrained outer shell and access is through an opening in the shell, since the flexibility of the conduit is limited by the geometry of the rigid tube-like sections and the plurality of joints. Finally, the length of such a conduit is limited by practical considerations to about eight feet.
Although a jointed high-pressure conduit such as that disclosed in U.S. Pat. No. 4,362,324 is successful in connecting the pressure source to the mandrel for repetitive swaging of a succession of tubes, there exists a continuing need for a more flexible high-pressure conduit which provides the advantages of the jointed conduit and avoids its limitations and disadvantages. The present invention fills this need, and further provides related advantages.